The invention relates to a device for displaying digital information as a set of pixels which are arranged according to a line pattern in a two-dimensional area, comprising a display memory for the storage of the display information, the information containing m bits for each pixel (m&gt;1), a data output of said display memory being connected to an address input of a programmable color map memory which comprises a data output for color information.
A device of this kind is known from British Patent Application No. 2,032,740.
The display memory and the color map memory of this device are controlled by means of a processor. A pixel on the screen of a display apparatus connected to the data output of the color map memory is formed by an m-bit data word from the display memory. This data word indicates an address in the color map memory. At this address a selected color is programmed, with the result that the pixel is displayed on the display apparatus in the selected color. Suitable programming of the color map memory enables the display apparatus to display the color information which is identified by only one or some of the m bits of the pixel. When used for the pixels of a picture to be displayed, this technique is referred to as picture page selection. Each picture page thus produced then has a depth of one or more bits. When another page is to be selected for display, it is necessary to completely reprogram the color map memory by means of the processor. This is a complex and time-consuming operation, particularly when the color map memory has a large content. In the described device it is also necessary to read the entire content of the color map memory in order to establish which page is displayed.